Magnetic separator



Feb. 11, 1969 R. w. SALMI 3,426,897 MAGNETIC SEPARATOR Filed Dec. 1, 1966 TTa-l l/VVE/VTO/P ROBERT W. SAL M/ BIN/6,

Attorney United States Patent 3,426,897 MAGNET C SEPARATOR Robert W. Salmi, Mountain Iron, Minn., assignor to United States Steel Corporation, a corporation of Delaware Filed Dec. 1, 1966, Ser. No. 598,257

US. Cl. 209-223 Int. Cl. B03c 1/14 4 Claims ABSTRACT OF THE DISCLOSURE drum length. This prevents too much magnetic material from accumulating near the ends of the drum and causing excessive wear.

This invention relates to an improved magnet construction for a magnetic separator.

One conventional type of magnetic separator includes a rotating drum and stationary magnets and pole pieces or shoes housed within the drum. The magnets and pole pieces or shoes project a field of magnetic attractive force through the drum surface over an area which extends across the width and is parallel to the drum surface This magnetic field is present in only a portion of the circumference through which the drum cover rotates. Magnetic and nonmagnetic particles can be continuously introduced to this area of magnetic attractive force Where separation occurs because the movement of nonmagnetic materials is according to gravitational and/ or centrifugal forces, but magnetic particles are attracted and held to the rotating drum surface until they'are carried beyond the area of magnetic attractive force. The attractive force of a magnet is defined as:

F: (KB)B/X where F=the pull on a small volume of ferromagnetic material,

K=a variable coefficient depending on the shape and volume of the particular ferromagnetic volume and on the physical arrangement of poles,

B=the flux density or gauss reading at the point in question, and

B/X=the slope of the flux-density (or field gradient) at the point in question.

One ditliculty with this type of separator is that the magnetic attractive force is not uniform along the length of the drum, but is greater near each end than toward the middle. Consequently the end portions of the drum attract more than their share of magnetic particles and with greater force, whereby the end portions wear more rapidly. The problem is aggravated in installations in which there are several drums in series, since each drum tends to feed more and more paritcles to the end portions of the next.

An object of the present invention is to provide an improved internal construction for a magnetic separator drum whereby the attractive force at the ends of the drum is approximately equal to the average along the length of the drum.

A more specific object is to provide an improved internal construction by which the attractive force is modified near the ends of the drum to equalize it with the average, preferably by rounding the side edges of the pole pieces or shoes and/or tapering them, thus gradually 3,426,897 Patented Feb. 11, 1969 increasing the clearance between the drum cover and pole pieces or shoes near the ends of the drum.

In the drawing:

FIGURE 1 is an end elevational view with parts broken away of a magnetic separator drum which has permanent magnets and embodies my invention;

FIGURE 2 is a vertical section on line IIII of FIG- URE 1;

FIGURE 3 is and end elevational view similar to FIG- URE 1, but showing a drum which has electromagnets; and

FIGURE 4 is a FIGURE 3.

FIGURES l and 2 show a portion of a separator drum which includes a stationary shaft 10, an end wall 12 journaled on the shaft, and a cylindrical cover 13 fixed to the end wall. The shaft carries stationary permanent magnets 14 (for example Alnico, ceramic, or equivalent) and pole pieces 15 of magnetic material within the drum supported on hangers 16 and hanger plates 17. The pole pieces transmit magnetic lines of force from the magnets through the cover. The cover is of nonmagnetic material, such as brass or stainless steel. The drum forms part of an otherwise conventional magnetic separator to which mineral particles are fed, either wet or dry. The magnets attract magnetic particles in the feed to the rotating outer surface of the cover to the exclusion of nonmagnetic particles, thereby effecting a separation. Magnetic particles are released from the drum surface when they have been carried beyond the magnetic field.

The pole pieces of a conventional separator have sharp side edges adjacent the intersection of the end wall and cover. These edges concentrate the magnetic lines of force near the ends of the cover. An unduly large proportion of the magnetic particles in the feed are attracted to the end portions of the cover. The high attractive force and the excessive quantity of material cause these portions to wear more rapidly than the rest of the cover and also impedes movement of particles through these regions of the separator. In accordance with my invention, I intentionally weaken the magnetic force near the ends of the drum to an extent that the attractive force at the end portions approximately equals the average along the length of the drum. Preferably I accomplish this weakening by rounding the side edges and /or gradually tapering the pole piece 15 adjacent the intersection of the end wall 12 and cover 13, as indicated at 18 in FIGURE 2. Nevertheless I can obtain a similar effect by other means, such as using weaker or fewer magnets at the ends of the drum.

FIGURES 3 and 4 show a portion of a separator drum which includes a stationary shaft 20, an end wall 22 journaled on the shaft, and a cylindrical cover 23 fixed to the end wall. Housed within the drum is a stationary electromagnet, which includes a core 24, a winding 25, a back piece 26 and a shoe 27 of magnetic material, all supported on hangers 28. In accordance with my invention, I round the side edge of the shoe 27, as indicated at 29 in FIGURE 4, and taper the portion of the shoe leading to the rounded edge, as indicated at 30. In this man ner I weaken the magnetic force at the end portions of the drum as in the first embodiment. I can also obtain a similar effect by arranging the windings to produce a smaller attractive force at the end portions.

From the foregoing description it is seen that my invention affords a simple and effective internal construction for modifying the attractive force at the end portions of a magnetic separator drum, whereby the force is approximately equal along the length of the entire drum. In this manner wear of the shell is distributed more evenly, the life of the cover prolonged and the capacity of the separator increased.

vertical section on line IV-IV of While I have shown and described certain preferred embodiments of my invention, it is apparent that other modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. In a magnetic separator which includes a drum, magnets housed within said drum, and members of magnetic material between said magnets for transmitting magnetic attractive force through said drum, said members extending in a direction parallel with the axis of said dnum, the combination therewith of means within said drum modifying the attractive force at the end portions of the drum in relation to the attractive force in the intermediate portions so that the attractive force at the end portions is approximately equal to the average along the drum length.

2. In a magnetic separator which includes a rotatable drum, stationary magnets housed within said drum, and

members of magnetic material between said magnets 20 for transmitting magnetic attractive force through said drum, the combination therewith of an internal construction for modifying the attractive force at the end portions of the drum comprising rounded side edges on said members adjacent the ends of the drum, the modifying action weakening the attractive force at the end portions of the drum to equal approximately the average along the drum length.

3. A construction as defined in claim 2 in which said magnets are permanent magnets, and said members are pole pieces.

4. A construction as defined in claim 2 in which said magnets are electromagnets and include windings and cores, and said members are shoes.

References Cited UNITED STATES PATENTS 451,369 4/ 1891 Conkling 209-2231 1,105,293 7/ 1914 Nathorst 209-219 1,324,529 12/1919 Ullrich 209-2231 2,945,590 7/1960 Stearns 209-219 X 3,279,602 10/1966 Kottenstette et al. 209-223 X HARRY B. THORNTON, Primary Examiner. T. R. MILES, Assistant Examiner. 

